Surface treatment agent for organic polymer substrates of polymerizable aerobic (meth)acrylate systems

ABSTRACT

The invention relates to surface treating agents for aerobic (meth)acrylate systems, which comprise one or more solvents, one or more (meth)acrylate monomers of the formula (A), wherein R═H or CH 3  and m=1-3, p=3-m and n=1-5, with m, p, and n being an integer, and one or more substances of formula (B), wherein R1, R2 and R3 are H, alkyl, cycloalkyl, aryl, alkylaryl, alkenyl or halogen and R4 is H, methyl or ethyl. The invention further relates to a surface treating agent for aerobic (meth)acrylate systems, which comprises one or more solvents, one or more (meth)acrylate monomers of the formula (A), one or more substances of the formula (B), and one or more additional (meth)acrylate monomers that are devoid of phosphorous functional groups. The invention also describes articles whose surface consists, at least in the boundary zone, of organic polymers and that were pretreated with the inventive surface treating agents.

TECHNICAL FIELD

The invention relates to a surface treatment agent to improve adhesionof aerobic (meth)acrylate systems to organic polymer substrates.

PRIOR ART

Reactive systems based on (meth)acrylates have important advantages. Inparticular, extremely rapidly reacting systems can be formulated andthey also generally have a very good adhesive range. Such reactivesystems are used in many different ways as adhesives, sealants,varnishes, and other coating agents. However, it seems that adhesion toorganic polymers, in particular polyamide substrates, is oftenproblematic.

Silanes are often used on glass and metals to improve adhesion of epoxyand polyurethane adhesives and coatings. As an example of this, we maymention work by Plueddemann (Plueddemann E. P. in “Silane CouplingAgents,” Plenum Press, New York, 1991, and Plueddemann E. P. in “Silanesand Other Coupling Agents,” Mital K. L., ed., VSP, Utrecht, 1992).

In studies of fracture surfaces, Clark (1988 Fall TechnicalMini-Seminar, November 2, Hyatt Regency Dearborn, Dearborn, Mich./ASC,The Adhesive and Sealant Council, Inc., Washington D.C., pp. 27-37)describes the advantageous application of methacryloxyethyl phosphateand bis(methacryloxyethyl phosphate) as primers for zinc, aluminum, andsteel for anaerobic methacrylate adhesives.

A primer for anaerobic adhesives is also described by U.S. Pat. No.4,731,146, where Cu(II), Co(II), Mn(II), Mn(III), or Cr(III) salts of anacid phosphate monomer are contained in a volatile solvent.

The anaerobic (meth)acrylate systems described have the majordisadvantage that they are suitable only for very small layerthicknesses, typically films. When applied as a thicker layer, incomparison, such adhesives have poor mechanical properties andconsequently very poor adhesion and [sic].

In order to improve adhesion of (meth)acrylate adhesives to preciousmetals, U.S. Pat. No. 6,265,508 describes a surface treatment solutionwhich, in addition to a polymerizable phosphoric acid ester monomer,also contains a polymerizable thiophenecarboxylic acid ester monomer.

Certain solvents can be used by themselves for bonding organic polymers.For example, poly(methyl methacrylate) parts treated with methylenechloride can be bonded together by contact and pressure. This method forbonding certain polymers, known as diffusion bonding, is however quitelimited and has major disadvantages. Since no adhesive is used, theparts must be made to fit each other exactly. In addition, this bondingworks only with solvents that are quite soluble in the organic polymer,which also means that after bonding, a considerable amount of solvent ispresent in the polymer, especially at the adhesive interface, leading tolocal weakening of the mechanical properties of the polymer.Furthermore, a very long time is required before the adhesive bondachieves its final strength. Finally, the solvents used are undesirablefor environmental and occupational hygiene reasons.

G. Habenicht (“Kleben [Adhesives],” Springer Verlag, Berlin, 1997, p.615) recommends concentrated formic acid or a formic acid/polyamidesolution as a pretreatment method to improve adhesion to polyamides. Butthis pretreatment has considerable limitations with regard to bothstability and occupational safety.

(Meth)acrylate systems are known that are called anaerobic. These are1-component systems that polymerize only when oxygen is excluded andthey are in contact with metal surfaces. An example of the applicationof such systems is to secure screws.

Two-component systems are defined as aerobic (meth)acrylate systemswhere, in addition to the (meth)acrylate monomers or mixtures thereofpresent in at least one component, one component contains at least oneradical initiator, typically a peroxide, and the other componentcontains at least one accelerator. In contrast to anaerobic systems,thick-layer bonds, coatings, and seals can be achieved with thesesystems.

DESCRIPTION OF THE INVENTION

The aim of this invention is therefore to overcome the describeddisadvantages and problems of surface treatment agents for organicpolymers. It was unexpectedly discovered that the disadvantages of theprior art can be eliminated by the surface treatment agent according tothe invention, as specified by claim 1 or claim 2. In particular, bymeans of the surface treatment agent for organic polymers according tothe invention, excellent adhesion of aerobic (meth)acrylate systems topolymers can be achieved, so that the bond between a (meth)acrylatesystem and a polymer breaks mainly cohesively within the (meth)acrylatesystem. The surface treatment agent has proven to be especially suitablefor polyamides.

This invention relates to a surface treatment agent for aerobic(meth)acrylate systems including one or more solvents as well as one ormore (meth)acrylate monomers of formula A, as well as one or moresubstances of formula B, or consisting of one or more solvents, one ormore (meth)acrylate monomers of formula A, one or more substances offormula B, as well as one or more additional (meth)acrylate monomersthat have no phosphorus-containing functional groups. Preferred solventsare selected from the group of chlorinated hydrocarbons, esters,alcohols, and ketones with boiling points <130° C. Acetone andisopropanol are particularly suitable. Particularly suitable variants ofthe (meth)acrylate monomers as specified by formula A have proven to be2-methacryloyloxy-ethyl phosphate, bis(2-methacryloyloxyethyl)phosphate,as well as tris(2-methacryloyloxyethyl)phosphate, or mixtures thereof.Particularly suitable variants of the substances as specified by formulaB have proven to be derivatives of resorcinol as well as monoalkylethers thereof.

EMBODIMENT OF THE INVENTION

This invention relates to a surface treatment agent for aerobic(meth)acrylate systems including one or more solvents as well as one ormore (meth)acrylate monomers of formula A, as well as one or moresubstances of formula B, or consisting of one or more solvents, one ormore (meth)acrylate monomers of formula A, one or more substances offormula B, as well as one or more additional (meth)acrylate monomersthat have no phosphorus-containing functional groups:

-   -   A: [1st display formula on German p. 4]    -   with R═H or CH₃, m=1-3, p=3-m, and n=1-15.    -   B: [2nd display formula on German p. 4]    -   wherein R1, R2 and R3 are each H, alkyl, cycloalkyl, aryl,        alkylaryl, alkenyl, or halogen and R4=H, methyl, or ethyl.

The solvent used has a boiling point <130° C. under standard conditions.Preferably a solvent with boiling point <100° C., particularlypreferably <90° C., is used. Suitable solvents are, for example,chlorinated hydrocarbons such as methylene chloride, 1,2-dichlorethane,1,2-dichlorethane, 1,1,1-trichlorethane, or trichlorethylene, esterssuch as butyl acetate, propyl acetate, ethyl acetate, ethyl formate, orbutyl formate, alcohols such as methanol, ethanol, n-propanol,isopropanol, or butanol, and also alkoxy alcohols such as alkoxypropanol, ethylene glycol monomethyl ether, ethylene glycol diethylether, or propylene glycol monomethyl ether, and ketones such as diethylketone, methyl ethyl ketone or methyl propyl ketone. Isopropanol andacetone have proven to be especially suitable.

The surface treatment agent according to the invention contains(meth)acrylate monomers of formula A

-   -   A: [display formula on German p. 5]

Here the radical R represents an H or a methyl group, where the methylgroup is preferred. The monomers include molecules with n from 1 to 15,preferably molecules with n from 1 to 3. Examples of this are2-(meth)acryloyloxyethyl phosphate, 4-(meth)acryloyloxybutyl phosphate,6-(meth)acryloyloxyhexyl phosphate, 8-(meth)acryloyloxyoctyl phosphate,10-(meth)acryloyloxydecyl phosphate, 16-(meth)acryloylhexadecylphosphate. Molecules with n=1 are preferred.

All possible combinations corresponding to the indices m=1-3 and p=0-2are conceivable, where at least one (meth)acrylate radical must bepresent. Preferred monomers are 2-methacryloyloxyethyl phosphate,bis(2-methacryloyloxyethyl)phosphate, as well astris(2-methacryloyloxyethyl)phosphate. Traces of phosphoric acid, ofcourse, may also be present as an impurity from the preparation of thesemonomers.

In certain cases, other (meth)acrylate monomers may also be presentwhich have no phosphorus-containing functional groups. In particular,these are monomers selected from the group of trimethylolpropanetriacrylate as well as ethoxylated and propoxylated (meth)acrylates. Theethoxylated and propoxylated (meth)acrylates can contain one or more(meth)acrylate groups, where one to three such groups are preferred.Especially preferred are ethoxylated trimethylolpropane triacrylate,propoxylated neopentyl glycol di(meth)acrylate, as well as ethoxylatedethyl (meth)acrylate, for example 2-(2-ethoxyethoxy)ethyl acrylate.(Meth)acrylate monomers of formula A are usually commercially suppliedas a mixture with such (meth)acrylate monomers.

These (meth)acrylate monomers, which have no phosphorus-containingfunctional groups, may be present in a concentration of 0-20 wt. %, inparticular 0-10 wt. %, calculated on the basis of the total formulation.

A preferred embodiment of the surface treatment agent contains(meth)acrylate monomers of formula A in a concentration of 1-10 wt. %,particularly preferably 2-7 wt. %, calculated on the basis of the totalformulation.

The surface treatment agent according to the invention containssubstances of formula B:

-   -   B: [display formula on German p. 6]

The radicals R1, R2 and R3 represent H, alkyl cycloalkyl [sic, should bealkyl, cycloalkyl], aryl, alkenyl, or halogen, and R4=H, methyl, orethyl. R1 and R2 and R3 can each be individually different, or any twomay be identical, or all three may be identical. The substituents R1,R2, and R3 can certainly also be connected with each other by a bridgeand can be saturated, unsaturated, or aromatic in nature, such as forexample for 1,3-dihydroxynaphthalene or1,3-dihydroxy-5,6,7,8-tetrahydronaphthalene. In another preferredvariant, the substituents represent R1=R3=H and R2=H or alkyl, inparticular H or alkyl with chain lengths from C1 to C12. Monomethylethers are particularly preferred. Resorcinol (1,3-dihydroxybenzene) hasproven to be particularly suitable (R1=R2=R3=R4=H).

The substances of formula B can be present alone or as a mixture in thesurface treatment agent. Calculated on the basis of the totalformulation, the concentration of the substance specified by formula Bis 1-10 wt. %, preferably 2-7 wt. %.

A preferred embodiment of the surface treatment agent can containorganosilicon compounds. These include compounds of formula CC: X—Si(OM)_(a)X′_(b)

with M=methyl or ethyl, X=C1-C18 alkyl, C1-C18 alkylene,3-(meth)acryloyloxypropyl, (meth)acryloyloxyalkylpropyl, or3-glycidyloxypropyl 3-mercaptopropyl [sic, probably should be3-glycidyloxypropyl, 3-mercaptopropyl], X′=H or CH3, and a=1-3 andb=3-a. The compounds vinyltrimethoxysilane, vinyltriethoxysilane,3-(meth)acryloyloxypropyltrimethoxysilane,3-(meth)acryloyloxypropyltriethoxysilane,3-mercaptopropyltrimethoxysilane, and 3-mercaptopropyltriethoxysilaneare preferred.

The organosilicon compound content is preferably 0-2 wt. %, particularly0-1 wt. %, calculated on the basis of the total formulation.

A preferred embodiment of the surface treatment agent can also containprocessing aids well known to those skilled in the art, such asadditives and fillers.

The invention additionally relates to an article for which the surfaceis made of organic polymers, at least in the area of the bond, and whichhas been pretreated with a surface treatment agent described above. Thearticle can be made entirely of organic polymers or alternatively can becoated with organic polymers or be bonded adhesively or otherwise. Theterm “organic polymer” here includes polymers and copolymers as well asblends of epoxy resins, carbonates, (meth)acrylates, acrylonitrile,styrene, vinyl chloride, butadiene, esters, and amides. Polyamides arepreferred, in particular Polyamide 6, Polyamide 6.6, Polyamide 11, andPolyamide 12, as well as mixtures thereof.

Improved adhesion can also possibly be achieved on certain metalsubstrates using the surface treatment agent. The surface treatmentagent has proven to be especially suitable for galvanized andzinc-plated steel.

The surface treatment agent is applied to the article. It can be appliedby spraying, dipping, or wiping with wetted carrier materials such ascloths, cotton wads, rollers, brushes, sponges, and the like. Thesurface treatment agent should be applied at least in the area where theadhesive or sealant is to be subsequently applied. In order to achievethe best possible adhesive bond, the surface treatment agent should beapplied as completely and uniformly as possible to the surfaces to bebonded. A certain time interval elapses between application of thesurface treatment agent and application of the adhesive or sealant,during which time the solvent can evaporate. Too short an open time mustbe avoided, since excess solvent has a negative effect on the mechanicalproperties of the adhesive or sealant. The open time for the surfacetreatment agent according to the invention is typically between 30seconds and a few hours. After the surface treatment agent hasair-dried, an aerobic adhesive or an aerobic sealant is applied to thelatter by a method well known to those skilled in the art.

Two-component systems are defined as aerobic (meth)acrylate systemswhere, in addition to the (meth)acrylate monomers or mixtures thereofpresent in at least one component, one component contains at least oneradical initiator, typically a peroxide, and the other componentcontains at least one accelerator. In contrast to anaerobic systems,these systems enable thick-layer bonds, coatings, and seals.

Such aerobic adhesives and sealants are two-component. Acrylate and/ormethacrylate monomers or mixtures thereof can be present in bothcomponents. But it is also quite possible that they are present in onlyone component. At least one accelerator is present in one component andat least one radical initiator, usually a peroxide, is present in thesecond component. Both components are mixed before use.

An adhesive is applied to the air-dried surface treatment agent and isthen bonded to at least one other article. If the surface of thatarticle is also made of organic polymers, it is advantageous for thatsurface to be pretreated with the surface treatment agent at least inthe area of the bond. If the surface of the other article is not made oforganic polymers, then such pretreatment can be optionally omitted.Alternatively, however, another type of surface treatment may then benecessary for this purpose.

In an application as a sealant, an opening in one article or betweenseveral articles is to be sealed in such a way that after polymerizationof the sealant, inlet or outlet of liquids or gases through the articlesis prevented. If the surface of the other article is also made oforganic polymers, it is advantageous for it to also be pretreated withthe surface treatment agent at least in the area of the bond. If thesurface of the other article is not made of organic polymers, then suchpretreatment can be optionally omitted, or else another type of surfacetreatment may be necessary for this purpose.

EXAMPLES Composition of Examples of the Surface Treatment Agent

The following compositions were prepared, based on isopropanol and theadhesion promoter Sartomer SR 9050 (commercial mixture of a 50% solutionof formula A in a (meth)acrylate, available from Sartomer/Cray Valley)as well as a substance as specified by formula B:

TABLE 1 Surface treatment agent compositions Compositions in wt. % NameRef. STA-3 STA-A1 STA-A2 STA-A3 STA-A4 STA-A5 IPA 100 94 94 94 94 94 94SR 9050 — 6 3 3 2 2 2 Resorcinol — — 3 — 3 3 3 Resorcinolmonomethylether — — — 3 — — — 3-Glycidyloxypropyltrimethoxysilane — — —— 1 — — 3-(Meth)acryloyloxypropyltrimethoxysilane — — — — — 1 —3-Mercaptopropyltrimethoxysilane — — — — — — 1 Total 100 100 100 100 100100 100[STM=surface treatment agent; IPA=isopropyl alcohol]

Substrates

The following substrates, commercially available from Rocholl (Germany),were used:

Polyamide 6: 100×25 mm, 4 mm thick

Polyamide 6.6: 100×25 mm, 4 mm thick

Polyamide 11: 100×25 mm, 3 mm thick

Polyamide 12: 100×25 mm, 4 mm thick

Surface Treatment Agent—Application

The surface treatment agent was applied to the polymer. Isopropanol wasused as the reference. The time between application of the surfacetreatment agent and the adhesive was at least 30 seconds.

Adhesive

All measurements were used [sic, should be made] with the adhesiveSikaFast® 5211 (commercially available from Sika AG, Switzerland). Thisis a fast-curing and flexible 2-component adhesive, where component Aessentially consists of (meth)acrylate monomers and component B consistsof a peroxide. The adhesive was premixed using a cartridge gun, mixedwith a static mixer, and applied.

Preparation of Test Pieces

Tensile shear strength test pieces were made as specified by DIN EN 1465from two pieces of polymer. The overlap was 12.5 mm; the adhesive layerthickness was 1.5 mm.

Testing

The tensile shear strength was measured on a Zwick tester with a pullrate of 10 mm/min according to DIN EN 1465, about one day afterapplication of the adhesive.

For measurements after poultice treatment, the test pieces were wrappedin a moist cloth and placed in a plastic bucket additionally containingan open vessel filled with water. The bucket was tightly sealed andstored for 7 days at 70° C. Then the test pieces were removed from themoist cloth, their surfaces were dried off with a paper towel, and theywere cooled down at room temperature and tested within a day.

Results

The results are compiled in Table 2, showing the effect of the surfacetreatment agent at room temperature on the tensile shear strengths. Noteon the one hand the effect of the surface treatment agent on theimprovement of adhesion and on the other hand the improvement of thefracture pattern, especially after poultice storage.

TABLE 2 Tensile shear strengths on untreated or treated polymers [MPa] *Ref. STA-3 STA-A1 STA-A2 STA-A3 STA-A4 STA-A5 PA-6 3 5  8  8  9  9  9(adh.) (mixed) (coh.) (coh.) (coh.) (coh.) (coh.) PA-6 3 3  4  5  4  3 6 poultice (adh.) (adh.) (coh.) (coh.) (coh.) (mixed) (coh.) PA-6.6 5 810 10 10 10 10 (adh.) (mixed) (mixed) (mixed) (mixed) (mixed) (coh.)PA-6.6 1 1  5  5 poultice (adh.) (adh.) (coh.) (coh.) PA-11 1  6 (adh.)(coh.) * Key: adh. = adhesive fracture; coh. = cohesive fracture; mixed= mixed fracture[STA=surface treatment agent]

1. Surface treatment agent for aerobic (meth)acrylate systems,comprising one or more solvents one or more (meth)acrylate monomers offormula A:

wherein R is H or a CH₃, and wherein m is an integer of 1, 2 or 3, p isan integer of 3-m, and n is an integer of from 1-15; one or moresubstances of formula B:

wherein R1, R2 and R3 are each H, alkyl, cycloalkyl, aryl, alkylaryl, orhalogen and R4 is H, a methyl, or an ethyl group.
 2. Surface treatmentagent as in claim 1, wherein the solvent has a boiling point understandard conditions that is less than 130° C.
 3. Surface treatment agentas in claim 1, wherein the solvent is a ketone or an alcohol.
 4. Surfacetreatment agent as in claim 1, wherein the solvent is isopropanol. 5.Surface treatment agent as in claim 1, wherein in formula A, n is 1, 2or
 3. 6. Surface treatment agent as in claim 1, wherein in formula A, Ris CH₃.
 7. Surface treatment agent as in claim 1, wherein theconcentration of (meth)acrylate monomers of formula A is 1-10 wt. %,calculated on the basis of the total formulation.
 8. Surface treatmentagent as in claim 1, wherein in formula B, R1, R2, and R3 is H or alkylgroup.
 9. Surface treatment agent as in claim 1, wherein in formula B,R1 and R3 is H, and R2 is H or alkyl group.
 10. Surface treatment agentas in claim 1, wherein in formula B, R4 is a methyl group.
 11. Surfacetreatment agent as in claim 1, wherein the concentration of the one ormore substances of formula B is 1-10 wt. %, calculated on the basis ofthe total formulation.
 12. Surface treatment agent as in claim 1,wherein the composition further comprises an organosilicon compound. 13.Surface treatment agent as in claim 12, wherein the concentration of theorganosilicon compound is 0-2 wt. %, calculated on the basis of thetotal formulation.
 14. Article comprised of the surface treatment agentof claim 1, wherein at least a bonding area of a surface of the articleis made of an organic polymer pretreated with the surface treatmentagent of claim
 1. 15. Article as in claim 14, wherein the organicpolymer is a polyamide selected from the group consisting of polyamide6, polyamide 6.6, polyamide 11, polyamide 12, and mixtures thereof. 16.Adhesive system, wherein the article of claim 14 is bonded to at leastone other article via an aerobic (meth)acrylate adhesive.
 17. Sealantsystem, wherein an opening the article of claim 14 or between two ormore of the articles of claim 14 is sealed against liquid or gaseousmaterials via an aerobic (meth)acrylate sealant.
 18. A method forimproving adhesion to organic polymer substrates, the method comprisingapplying surface treatment agent of claim 1 to at least one surface ofthe organic polymer substrates.
 19. Surface treatment agent for aerobic(meth)acrylate systems, consisting of one or more solvents one or more(meth)acrylate monomers of formula A:

wherein R is H or a CH₃, and m wherein m is an integer of 1, 2 or 3, pis an integer of 3-m, and n is an integer of from 1-15; one or moresubstances of formula B:

wherein R1, R2 and R3 are each H, alkyl, cycloalkyl, aryl, alkylaryl, orhalogen and R4 is H, methyl group, or a ethyl group; and one or moreadditional (meth)acrylate monomers that have no phosphorus-containingfunctional groups.
 20. Surface treatment agent as in claim 19, whereinthe (meth)acrylate monomers having no phosphate-containing functionalgroups are selected from the group consisting of trimethylolpropanetriacrylate, ethoxylated methacrylates, and propoxylated(meth)acrylates.
 21. Surface treatment agent as in claim 19, wherein theadditional (meth)acrylate monomers having no phosphorus-containingfunctional groups are present in a percentage in the range from 0-20 wt.%, calculated on the basis of the total formulation.